460 research outputs found
Optical properties of planar chiral meta-materials
The polarization state of visible light is found to be altered upon reflection from artificial two-dimensional chiral media. Arrays of metallic planar chiral structures were fabricated by electron beam lithography and ion beam milling. The characteristic dimensions on the chiral elements correspond to wavelengths in the near-IR. Our chiral media are found to induce strong polarization effects, with the handedness of individual elements having a direct effect on the sense and magnitude of rotation of the diffracted light
Stretchable liquid-crystal blue-phase gels
Liquid crystalline polymers are materials of considerable scientific interest
and technological value to society [1-3]. An important subset of such materials
exhibit rubber-like elasticity; these can combine the remarkable optical
properties of liquid crystals with the favourable mechanical properties of
rubber and, further, exhibit behaviour not seen in either type of material
independently [2]. Many of their properties depend crucially on the particular
mesophase employed. Stretchable liquid crystalline polymers have previously
been demonstrated in the nematic, chiral nematic, and smectic mesophases [2,4].
Here were report the fabrication of a stretchable gel of blue phase I, which
forms a self-assembled, three-dimensional photonic crystal that may have its
optical properties manipulated by an applied strain and, further, remains
electro-optically switchable under a moderate applied voltage. We find that,
unlike its undistorted counterpart, a mechanically deformed blue phase exhibits
a Pockels electro-optic effect, which sets out new theoretical challenges and
new possibilities for low-voltage electro-optic devices.Comment: 15 pages, 6 figures, additional data and discussion included.
Supplementary videos available from F. Castles on reques
Measuring our universe from galaxy redshift surveys
Galaxy redshift surveys have achieved significant progress over the last
couple of decades. Those surveys tell us in the most straightforward way what
our local universe looks like. While the galaxy distribution traces the bright
side of the universe, detailed quantitative analyses of the data have even
revealed the dark side of the universe dominated by non-baryonic dark matter as
well as more mysterious dark energy (or Einstein's cosmological constant). We
describe several methodologies of using galaxy redshift surveys as cosmological
probes, and then summarize the recent results from the existing surveys.
Finally we present our views on the future of redshift surveys in the era of
Precision Cosmology.Comment: 82 pages, 31 figures, invited review article published in Living
Reviews in Relativity, http://www.livingreviews.org/lrr-2004-
Spin-photon interface and spin-controlled photon switching in a nanobeam waveguide
Access to the electron spin is at the heart of many protocols for integrated
and distributed quantum-information processing [1-4]. For instance, interfacing
the spin-state of an electron and a photon can be utilized to perform quantum
gates between photons [2,5] or to entangle remote spin states [6-9].
Ultimately, a quantum network of entangled spins constitutes a new paradigm in
quantum optics [1]. Towards this goal, an integrated spin-photon interface
would be a major leap forward. Here we demonstrate an efficient and optically
programmable interface between the spin of an electron in a quantum dot and
photons in a nanophotonic waveguide. The spin can be deterministically prepared
with a fidelity of 96\%. Subsequently the system is used to implement a
"single-spin photonic switch", where the spin state of the electron directs the
flow of photons through the waveguide. The spin-photon interface may enable
on-chip photon-photon gates [2], single-photon transistors [10], and efficient
photonic cluster state generation [11]
Tinnitus referral pathways within the National Health Service in England: a survey of their perceived effectiveness among audiology staff
<p>Abstract</p> <p>Background</p> <p>In the UK, audiology services deliver the majority of tinnitus patient care, but not all patients experience the same level of service. In 2009, the Department of Health released a Good Practice Guide to inform commissioners about key aspects of a quality tinnitus service in order to promote equity of tinnitus patient care in UK primary care, audiology, and in specialist multi-disciplinary centres. The purpose of the present research was to evaluate utilisation and opinions on pathways for the referral of tinnitus patients to and from English Audiology Departments.</p> <p>Methods</p> <p>We surveyed all audiology staff engaged in providing tinnitus services across England. A 36-item questionnaire was mailed to 351 clinicians in all 163 National Health Service (NHS) Trusts identified as having a tinnitus service. 138 clinicians responded. The results presented here describe experiences and opinions of the current patient pathways to and from the audiology tinnitus service.</p> <p>Results</p> <p>The most common referral pathway was from general practice to a hospital-based Ear, Nose & Throat department and from there to a hospital-based audiology department (64%). Respondents considered the NHS tinnitus referral process to be generally effective (67%), but expressed needs for improving GP referral and patients' access to services. 'Open access' to the audiology clinic was rarely an option for patients (9%), nor was the opportunity to access specialist counselling provided by clinical psychology (35%). To decrease the number of inappropriate referrals, 40% of respondents called for greater awareness by referrers about the audiology tinnitus service.</p> <p>Conclusions</p> <p>Respondents in the present survey were generally satisfied with the tinnitus referral system. However, they highlighted some potential targets for service improvement including 1] faster and more appropriate referral from GPs, to be achieved through education on tinnitus referral criteria, 2] improved access to psychological services through audiologist training, and 3] ongoing support from tinnitus support groups, national charities, or open access to the tinnitus clinic for existing patients.</p
Understanding Galaxy Formation and Evolution
The old dream of integrating into one the study of micro and macrocosmos is
now a reality. Cosmology, astrophysics, and particle physics intersect in a
scenario (but still not a theory) of cosmic structure formation and evolution
called Lambda Cold Dark Matter (LCDM) model. This scenario emerged mainly to
explain the origin of galaxies. In these lecture notes, I first present a
review of the main galaxy properties, highlighting the questions that any
theory of galaxy formation should explain. Then, the cosmological framework and
the main aspects of primordial perturbation generation and evolution are
pedagogically detached. Next, I focus on the ``dark side'' of galaxy formation,
presenting a review on LCDM halo assembling and properties, and on the main
candidates for non-baryonic dark matter. It is shown how the nature of
elemental particles can influence on the features of galaxies and their
systems. Finally, the complex processes of baryon dissipation inside the
non-linearly evolving CDM halos, formation of disks and spheroids, and
transformation of gas into stars are briefly described, remarking on the
possibility of a few driving factors and parameters able to explain the main
body of galaxy properties. A summary and a discussion of some of the issues and
open problems of the LCDM paradigm are given in the final part of these notes.Comment: 50 pages, 10 low-resolution figures (for normal-resolution, DOWNLOAD
THE PAPER (PDF, 1.9 Mb) FROM http://www.astroscu.unam.mx/~avila/avila.pdf).
Lectures given at the IV Mexican School of Astrophysics, July 18-25, 2005
(submitted to the Editors on March 15, 2006
Bayesian analysis of cosmic structures
We revise the Bayesian inference steps required to analyse the cosmological
large-scale structure. Here we make special emphasis in the complications which
arise due to the non-Gaussian character of the galaxy and matter distribution.
In particular we investigate the advantages and limitations of the
Poisson-lognormal model and discuss how to extend this work. With the lognormal
prior using the Hamiltonian sampling technique and on scales of about 4 h^{-1}
Mpc we find that the over-dense regions are excellent reconstructed, however,
under-dense regions (void statistics) are quantitatively poorly recovered.
Contrary to the maximum a posteriori (MAP) solution which was shown to
over-estimate the density in the under-dense regions we obtain lower densities
than in N-body simulations. This is due to the fact that the MAP solution is
conservative whereas the full posterior yields samples which are consistent
with the prior statistics. The lognormal prior is not able to capture the full
non-linear regime at scales below ~ 10 h^{-1} Mpc for which higher order
correlations would be required to describe the matter statistics. However, we
confirm as it was recently shown in the context of Ly-alpha forest tomography
that the Poisson-lognormal model provides the correct two-point statistics (or
power-spectrum).Comment: 11 pages, 1 figure, report for the Astrostatistics and Data Mining
workshop, La Palma, Spain, 30 May - 3 June 2011, to appear in Springer Series
on Astrostatistic
- …